Circuit arrangement for ultra short waves



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CIRCUIT ARRANGEMENT FOR ULTRA SHORT WAVES Filed March 25, 1943 \o 70F/L.

v l HiAr//VG SUP/3L Y IN V EN TOR.

Patented Jan. 13, 1948 CIRCUIT ARRANGEMEN T FOR ULTRA SHORT WAVESMaximiliaan Julius Otto Strutt,

Eindhoven,

Netherlands, assignor to Hartford National Bank & Trust Co., Hartford,Conn., as trustee Application March 23, 1943, Serial No. 480,197 In theNetherlands January 28, 1941 Section 1, Public Law 690, August 8, 1946Patent expires January 28, 1961 4 Claims. (Cl. Z50-20) This inventionrelates to a circuit arrangement for ultra-short waves which comprises aresonant circuit mainly consisting of two parallel conductors, forinstance a tunable Lecher-wire syst-ern, and an electron discharge tubewhich may serve for amplifying, mixing or detecting purposes.

More particularly, in mixing circuit arrangements for the reception ofultra-short waves, it is often advantageous to connect the cathode ofthe electron discharge tube to a point of a resonant circuit which isnot earthed for high frequency. In such a circuit, however, disturbancesoccur when the cathode of the said electron discharge tube is indirectlyheated by means of a filament which is fed from a supply earthed forhigh frequency, the said disturbances being audible as crackling orhumming noises after detection of the high frequency oscillations.

One of the objects of the invention is to provide means by which thesaid disturbances, due to the high frequency voltage set up between thelament and the cathode of the electron discharge tube, can be avoided ina simple manner in arrangements of the kind referred to above.

To this end, according to the invention, the supply conductors for thefilament between a point earthed for high frequency and the point of theresonant circuit connected to the cathode of the electron discharge tubeare tightly coupled throughout their length for high frequency currentsto the part of the resonant circuit conductors located between the twopoints in such manner that between the cathode and the lament of thetube there occur at least substantially no alternating voltages having afrequency whose order of magnitude corresponds to the natural frequencyof the resonant circuit.

The said close coupling for high frequency currents can be realized byarranging for the supply conductors between the said points cf theresonant circuit, with the interposition of insulating material, toextend along the surface of the reso nant circuit conductors, which maybe shaped as a band, or within the tubular resonant circuit conductors,thus establishing a capacitative coupling between the supply andresonant circuit conductors and avoiding the appearance of disturbinghigh frequency voltages between corresponding points of the conductors.

In another suitable form of construction of the circuit, according tothe invention, at least one of the supply conductors is constituted byone or by both resonant circuit conductors or by a part thereof.

reference to the accompanying drawing representing, by way of example, aparticularly suitable form of construction of a push-pull mixing circuitaccording thereto.

The circuit represented in the drawing com nected triode systems producethe local oscillations, to which end the control grid circuits comprisea Lecher-wire system 8 which can be tuned by means of an earthed bridge25, the anode cir- Y cuits including a resonant circuit 9 and the cath-The invention will be more fully explained by ode circuit comprising atunable Lecher-wire system I0, I0', I0", all of which circuits are tunedto the frequency of the local oscillations.

Between the two diode anodes is interposed a resonant circuit II whichis tuned to the frequency of the incoming oscillations supplied to thiscircuit through the intermediary 0f a coupling coil l2.

The anodes of the triode systems are connected through a resistance 2|to the positive terminalv of a source of anode voltage (not represented)whose negative terminal may be earthed.

The cathodes B, I of the two triode systems 2, 3 are connectedrespectively to the ends of the resonant circuit constituted by theparallel conductors I and I0' and the bridge ID", the centre of thebridge I0" for tuning the circuit being connected to earth thrcugh theseries connection ofV a resonant circuit I4 tuned to the intermediatefrequency and a network I5 which serves to produce a suitable diode biasand consists of the parallel connection of a resistance and a condenser.

In the circuit illustrated, the cathodes '6 and I of the tube I conveyalternating voltages having the frequency of the local oscillations withrespect to earth so that, if the cathodes are indirectly heated bylaments I6, I'I connected to an earthed supply, alternating voltagesalso occur between each of the two cathodes and the associated lament,which voltages cause. unde-l` sirable disturbances, as has already beensaid'-v above.

According to one aspect of the invention, the occurrence of thesedisturbances in the circuit illustrated is avoided by supplying theheating Voltage Egi, in the case under review an alternating voltage, tothe laments IB, Il through conductors coupled to the resonant circuitconductors between the point I8 of the resonant circuit I0, i8', l0"earthed for local oscillations and the ends of this circuit which areconnected to the cathodes. For this purpose, one end of each lament I6,I 1 is directly connected to the associated cathode 6, I respectivelyand through the intermediary ofthe resonant circuitconductorsv i0, lrespectively themselves and the point I8 of the bridge l0" to thejunction terminal I9 for the heating voltage, which terminal is earthedfor high frequency, whereas the other end ofv eachfilament is connectedto the junction terminal through conductors 2|, 2|' respectivelyinsulatingly arranged within the tubular resonant circuit conductors I0,I 0' respectively and aleadl in point 22 located similarly to pointi'of'the tubular bridge piece l0".

a choke 23 constituting a, high impedance to inf termediate frequencyoscillations.

By supplying the heating current to the filaments in the manner set outabove, the: occur rence of alternating voltages having a frequency whoseorder of magnitudecorresponds to the natural frequency of. the. resonantcircuit isV avoided withcertainty between cathode vand lament, thusremoving the cause of the said disturbances.

What I claim is:

1. A circuit for ultra short waves, more particularly a mixing circuit,comprising a resonant circuit which includes twor parallel conductors.

andan electron discharge tube having a filament, an indirectlyheatedcathode connected to a point on the resonant circuit whichis notearthed for.

between the cathode andithe filament of` the* tube there appear at leastsubstantially noalternating voltages having a frequency whose orderofmagnitude corresponds to the natural frequency of the resonant circuit.

2. A circuit for ultra short waves, as claimedy in claim 1, in whichsaid resonant circuit comprises tubular conductors and one or bothsupplyv conductors between thesaid points of theresonant circuit areprovided withinV saidtubularu con--H ductors.

3. A frequency mixer comprising` a pair'of` oscillator electrodestructures each including an;

indirectly heated cathode, a filament therefor, a:

grid and an anode, all located in a single evacuated envelope, a diodeanode cooperating with.

each cathodeand also located in'said envelope; tuned circuits coupled.betweenk corresponding, electrodes of said structures' and tuned to: thefrequency of the locally produced oscillations, said. cathode tunedcircuit comprising-a pair of par.-

allel tubular conductors one end of which isshunted byatubularconductor,,and the other.

Thesupply conductor: connected to the junction terminal I9 includes;

end of which is connected to said cathodes, one terminal of eachfilament being connected directly to its cathode, the other terminal ofeach filament being connected to a supply lead extending through theinterior. of that tubular conductor which is associated with itscathode, a connection from the center point of said shunting tubularconductor to one terminal of an alternating current filament supply, acondenser connecting said last terminal to ground for radio frequencyenergy, and a connection from the other terminal of said filament supplyto the supply leads in the interiors of said pair of tubular conductors,a tuned circuit coupled between said diode anodes and tuned to thefrequency of the input waves, and a circuit tuned to the difference ofthe frequency of the locally produced oscillations and the frequency ofthe input waves, said last circuit being located between the cathodetuned circuit and the diode anode tuned circuit.

4. A frequency mixer comprising a pair of oscillator electrodestructures each including an indirectly heated cathode, a filamenttherefor, a grid andan anode, a diode anode cooperating with eachcathode, tuned circuits coupled between corresponding electrodes of saidstructures and tuned to the frequency of the locally producedoscillations, said cathode tuned circuit comprising a pair of paralleltubular conductors one end of which is shunted by a tubular conductor,and the other end of which is connected to said cathodes, one terminalof each lament being connected directly to its cathode, the otherterminal of each filament being connected to a supply lead extendingthrough the interior of that tubular conductor which is associated withitsV cathode, a connection from the center point of said shuntingtubular conductor to one terminal of an alternating current .filamentsupply, a condenser connecting said last terminal to ground for radiofrequency energy, and a connection from the other terminal of saidfilament supply to the supply leads in the interiors of said pair oftubular conductors; a tuned circuit coupled between said diode anodesand tuned to the frequency of the input waves, and a circuit tuned tothe sum or difference frequency of the locally produced oscillations andthe'frequency of the input waves, said last circuit being coupled to thecenter point of said shunting tubular conductor.

MAXIMILIAAN JULIUS OTTO STRUTT.

REFERENCES CITED The following references are `of record in theV file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,097,514 Chaffee Nov. 2, 19372,236,004 MacLean Mar. 25, 1941V 2,272,062 George Feb. 3, 1942:2,285,372 Strutt et al June 2, 1942 FOREIGN PATENTS Number Country Date557,163" Great Britain Nov. 8,1943'

